Management of optical links using power level information

ABSTRACT

In an optical communication network, optical communication nodes exchange information detailing power level variations to support management and administration of optical communications. This exchange of information permits nodes to determine aggregate power level variations over light paths to support operations such as selection from available light paths and configuration of optical communication characteristics.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to optical communicationnetworks and, more particularly, to power level management in opticalnetworks.

BACKGROUND OF THE INVENTION

In typical synchronous optical network (SONET) systems, power levelmanagement is performed during the installation of a network, oftenmanually, and then re-optimized with the addition or deletion ofconnections in the network. By measuring the channel power levels andoptical signal-to-noise ratios at different points in the network, powerlevels at transmitters may be adjusted according to algorithms,improving the performance of the connections with smaller opticalsignal-to-noise at the cost of those connections with higher opticalsignal-to-noise. In addition, amplifiers often operate in an automaticlevel control (ALC) mode to minimize the impact of changes in span powerlosses. In this mode, changes in one channel's power level can influenceanother channel's power levels, thus complicating attempts to managepower levels. Because changes in particular power level parameters canaffect the settings of other power levels, administrators often employtime consuming, iterative processes to achieve power level balancing.

SUMMARY OF THE INVENTION

In accordance with the present invention, techniques for power levelmanagement in optical networks are provided.

According to a particular embodiment, a method for power levelmanagement of optical communications receives a request to establish acommunication channel with a remote optical node and determines aplurality of light paths to the remote optical node. For each of thelight paths, the method determines a next node for the light path to theremote optical node, determines add power level variation for the lightpath, generates a path setup message identifying the light path and theadd power variation, and communicates the path setup message to the nextnode.

According to a another embodiment, a method for power level managementof optical communications receives a path setup message identifying alight path between an add node and a drop node, the path setup messagecomprising a power level variation value, and determines whether achannel for the light path to a next node in the light path isavailable. If the channel is available, the method determines throughpower level variation for the light path, adds the through power levelvariation to the power level variation value in the path setup message,and communicates the path setup message to the next node in the lightpath.

According to a another embodiment, a method for power level managementof optical communications receives a plurality of path setup messagescorresponding to a plurality of light paths from a remote optical node,each of the path setup messages identifying one of the light paths andindicating a power level variation value for the identified light path.For each of the path setup messages, the method determines drop powerlevel variation for the light path identified in the path setup message,adds the drop power level variation to the power level variation valuein the path setup message to obtain an aggregate power level variationfor the identified light path, generates a setup reply messageindicating the identified light path and the aggregate power levelvariation for the light path, and communicates the setup reply messageto the remote optical node.

According to a another embodiment, a method for protection switching inan optical network detects failure of a light path, determines aprotection light path, determines drop power level variation for theprotection light path, generates a protection switch message identifyingthe protection light path and the drop power level variation, andcommunicates the protection switch message to a previous node on theprotection light path.

Embodiments of the invention provide various technical advantages. Usingthese techniques, networks may implement power level management morequickly than compared to previous techniques. This speed of operationprovides a number of advantages. For example, protection switching mayrequire rapid response in the event of a severed link. With thedisclosed techniques, power level management during protectionswitching, or even link restoration, can be implemented. Moreover, thepotential speed of these techniques may also support emerging opticaltechnologies, such as dynamically routed mesh networks.

In addition, these techniques can be implemented along with other and/orexisting power level management techniques. For example, thesetechniques may be used to provide quick power level management, withother techniques, such as iterative power level adjustments, used forfine-tuning of power level adjustments.

Other technical advantages of the present invention will be readilyapparent to one skilled in the art from the following figures,descriptions, and claims. Moreover, while specific advantages have beenenumerated above, various embodiments may include all, some, or none ofthe enumerated advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and itsadvantages, reference is now made to the following description, taken inconjunction with the accompanying drawings, in which:

FIG. 1 illustrates an optical communication system having nodes thatperform power level management in accordance with various embodiments ofthe present invention;

FIG. 2 illustrates a node from the optical communication system operableto perform power level management in accordance with various embodimentsof the present invention;

FIG. 3 illustrates a particular example of power level management in theoptical communication system;

FIG. 4 is a flowchart illustrating a method for performing power levelmanagement at an add node for a light path;

FIG. 5 is a flowchart illustrating a method for performing power levelmanagement at an intermediate node of a light path;

FIG. 6 is a flowchart illustrating a method for performing power levelmanagement at a drop node of a light path; and

FIG. 7 is a flowchart illustrating a method for performing power levelmanagement during protection switching.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an optical communication system, indicated generallyat 10, that includes optical nodes 12 forming an optical network 14,which provides for the transportation of information between variouselements such as communications devices 16. In general, nodes 12communicate to determine aggregate power level variations on light pathsto provide power level management for the light paths. Morespecifically, a selected node 12 (add node) attempting to establish alight path to another node 12 (drop node) may communicate with variousnodes 12 to determine power level variations on one or more light pathsfrom the add node to the drop node. The add node may use these lightpath power level variations to select and configure a light path to thedrop node through network 14.

Network 14 represents any suitable collection and arrangement ofelements providing for the communication of information in opticaltransmissions. This may include any appropriate electrical and opticalinterconnections to support the establishment of light paths forcommunication of information using circuit switched and/or packet basedprotocols. Each light path represents a communication channel spanningbetween two or more nodes 12. For example, according to particularembodiments, nodes 12 communicate information using wave-length divisionmultiplexed (WDM) protocols. Thus, in certain embodiments, two adjacentnodes 12 may potentially be linked by multiple available light paths,such as a light path on each channel.

Nodes 12 represent hardware, including suitable controlling logic,supporting the communication of information in optical transmissions.For example, nodes 12 may provide add drop multiplexer (ADM)functionality to add, propagate, and drop optical signals transmitted onlight paths. Each node 12 links using optical fibers to other nodes 12in network 14 and potentially to other communications equipment, such asdevices 16. In addition, each device 12 may link with othercommunications equipment, such as devices 12, using electricalcommunication channels to exchange management messages. For example,nodes 12 may exchange multi-protocol label switching (MPLS) messagesusing electrical communication channels. However, the system 10contemplates nodes 12 using any suitable optical, electrical, or othercommunication links to support communication of management messages forthe administration of optical communication links.

In the example illustrated, nodes 12 provide multiples routes (eachpotentially having multiple light paths) for optically transmittinginformation from a first device 16 (device A) to a second device 16(device B). However, the example provided illustrates only selectedelements and connections, and system 10 contemplates including anysuitable elements providing connectivity between any number and type ofcommunications equipment. Devices 16 represent any suitable equipmentfor the transmission and receipt of communications across opticalnetwork 14. For example, devices 16 may include gateways, switches,routers, and/or any other suitable communications equipment locatedwithin public or private networks.

In operation, nodes 12 provide power level management by exchangingpower variation information to determine aggregate power levelvariations across light paths. To enable rapid calculation of powerlevel variations for light paths, each node 12 maintains power levelinformation indicating power level variations for each potential path(add, drop, and through) for node 12. For example, consider node 12having sixty channels for optically transmitting information. Node 12will maintain power level variations for adding, dropping, and passingthrough optical signals at a wavelength for each channel. Thus, for thisexample, node 12 maintains one hundred eighty values for power levelvariations (sixty for adding signals, sixty for dropping signals, andsixty for passing through signals). In addition, nodes 12 may maintaintransmission power level variations measuring the variations in powercaused by the transmission of optical signals across optical fibers. Forexample, each node 12 can measure and/or maintain information indicatingthe amount of power level variation resulting as optical signalspropagate along optical fibers from adjacent nodes 12.

When establishing a link between an add mode and a drop node, nodes 12communicate to determine aggregate power level variations along one ormore light paths between the add node and the drop node. An aggregatepower level variation indicates the sum of the add power level variationat the add node, the drop power level variation at the drop node, andthrough power level variations at each of the intermediate nodes in alight path. Based upon the aggregate power level variations, the addnode selects a light path and configures to provide effectivecommunications on the selected light path. For example, the add node mayselect the light path with an aggregate power level variation closest toa target and then set variable attenuation for the wavelength of theselected light path to a value appropriate to compensate for thedetermined aggregate power level variation.

For example, consider device 16 labeled A (device A) with informationfor communication to device 16 labeled B (device B). To communicate thisinformation, network 14 may establish a link between node 12 labeled A(node A) and node 12 labeled B (node B). Thus, in this example, node Afunctions as an add node and node B functions as a drop node fortransmissions. Node A, upon receiving an appropriate indication toestablish a link with node B, such as a request from device A, initiatesa process to determine power level variations along one or more lightpaths between node A and node B. To initiate the process, node A mayfirst identify available light paths to adjacent nodes 12 on routes tonode B. For example, node A may determine currently available channelsto node C, node D, and node E. For each identified light path, node Adetermines the add power level variation, encodes this value into a pathsetup message, and communicates the setup message to the next node 12 onthe light path.

For example, for each available wavelength between node A and node C,node A may determine the add power level variation for the wavelength,encode the value within a path setup message, and communicate the pathsetup message to node C. Node A may perform similar operations foravailable wavelengths to node D and node E. Thus, node A may communicatesetup messages for multiple wavelengths to each of node C, node D, andnode E. However, system 10 contemplates node A combining or separatingthe setup messages into one or more messages communicated to each ofnode C, node D, and node E. For example, node A may communicate a setupmessage for each available wavelength to Node C, with each setup messageindicating the add power level variation within node A for thewavelength. Alternatively, node A may combine this information to reducethe number of setup messages communicated, such as by generating asingle path setup message indicating each of the available wavelengthsand, for each wavelength, the add power level variation within node A.

The path setup messages propagate along the paths between node A andnode B, aggregating power level variations along the way. Along a lightpath, each intermediate node 12 supplements the encoded power levelvariation in a path setup message with a value for through power levelvariation. For example, node C receives one or more path setup messagesfrom node A, with each message identifying a particular wavelength andspecifying a power level variation (the specified power level variationat this point reflects only the add power level variation of node A atthis wavelength). For each path setup message, node C determines whetherthe indicated wavelength is available to the next node 12 or nodes 12 inpaths to node B. If so, node C determines through power level variationsfor the wavelength, adds this value to the power level variation encodedin the path setup message, and forwards the message to the next node ornodes 12. Therefore, as a setup message propagates through network 14,it accumulates power level variation information from each traversednode 12.

Node B thus receives one or more path setup messages identifying some orall potential light paths from node A through Network 14. For eachmessage identifying a potential light path, node B determines drop powerlevel variation for the identified wavelength and adds this value to theaggregate power level variation from the path setup message. Thisaggregate power level variation then reflects the total of the add,through, and drop power level variations affecting the light path. NodeB replies to node A indicating the aggregate power level variations foreach of the potential light paths. As with other management messages,nodes 12 may use separate messages for each reply or combine two or morereplies into a single message. Regardless, these replies permit theoriginating node 12 (node A) to select between potential paths based onthe aggregate power level variations for these paths.

Upon receiving the replies, node A may use any suitable techniques forselecting between potential paths. According to particular embodiments,node A selects the potential path having a power level variation closestto a target value. This target may be zero or a non-zero value. Forexample, power level variations for light paths may have a typical oraverage value for which nodes 12 can be designed to accommodate. Thetarget value may reflect this “expected” power level variation. However,system 10 contemplates nodes 12 using any suitable algorithms, criteria,and techniques for selecting between potential light paths based uponaggregate power level variations.

Using the aggregate power level variation of the selected light path,node A can also adjust its operational characteristics. For example,Node A may adjust variable attenuation to accommodate the aggregatepower level variation along the selected light path to provide anacceptable signal for receipt by node B. However, nodes 12 may havelimited dynamic ranges that permit accommodation for only certainamounts of power level variation. If all of the potential light pathshave an aggregate power level variation that exceeds the capabilities ofthis dynamic range, node A may indicate failure in establishing the linkto node B.

According to particular embodiments, nodes 12 support protectionswitching using power level management techniques similar to thosedisclosed above. This leverages on the speed of these techniques topermit power level management in protection switching scenarios. In manyoptical systems, specifications dictate speeds at which protectionswitching must occur. For example, an optical system may requireprotection switching to occur in less than 50 milliseconds. According toparticular embodiments, the disclosed techniques permit power levelmanagement and protection switching to occur in less than 50milliseconds and potentially in less than 15 milliseconds. At thesespeeds, optical systems may even incorporate restoration in place ofprotection for severed links. In protection switching, a particularlight path is selected as backup for an active link. If the active linkfails, traffic is switched to the backup. In restoration, a new lightpath is selected from potential light paths on the failure of an activelink. Thus, restoration potentially chooses a more effective linkcompared to protection.

To provide protection switching, nodes 12 monitor active light pathsand, in the event of a failure, initiate switching of communications toa new light path. For example, consider a communications link betweennode A and node B along a light path routed over intermediate nodes Dand G. Further assume a protection light path is assigned along theroute of nodes C, F, and I. While the primary light path remains active,node B may monitor for failure. To monitor node B may use any suitabletechniques to detect failure of the light path, such as by detecting theabsence of light on the path.

Given a failure of the preliminary light path, node B initiatesswitchover to the backup light path. To effect the switch to the backuplight path, node B generates a switchover message and communicates themessage to node A along the route of the backup light path. Thus, theswitchover message traverses nodes I, F, and C to reach node A. Togenerate the switchover message, node B determines drop power levelvariation for the wavelength of the backup light path and encodes thisvalue within the switchover message. Then as the switchover messagepropagates to node A, each intermediate node 12 supplements the powerlevel variation information with appropriate values. Thus, nodes I, F,and C each add values for through power level variation at thewavelength specified for the backup light path. Therefore, node A maycalculate the aggregate power level variation for the backup light pathwith the addition of the add power level variation within node A to thepower level variation indicated in the received switchover message.Using this information, node A may configure its operation to provideacceptable signals along the backup light path. For example, asdiscussed above, node A may configure variable attenuation toaccommodate for the aggregate power level variation expected along thebackup light path.

In addition or as an alternative to providing protection switching,nodes 12 may support restoration of communications links upon failure ofa light path. For example, consider the previous description of afailure along a primary light path from node A to node B traversing apath through nodes D and G. Upon detecting a failure of the primarylight path, node B may initiate a restoration process using messagingsimilar to that described above with respect to provisioning of a newlight path. However, according to particular embodiments, the flow ofrestoration path messages propagates in reverse along available routesfrom node A to node B. For example, node B may determine all availablelight paths from node A and, for each available light path, generate arecovery path message that indicates drop power level variation withinnode B for the wavelength associated with the light path. As withpreviously discussed messages, each node 12 along the route of a lightpath supplements the included power level variation with appropriatevalues. Thus, node A may perform restoration by selecting among anynumber of potential light paths based on aggregate power levelvariations for the light paths.

While the preceding descriptions and examples focus on particularembodiments for provisioning, protection, and restoration of lightpaths, system 10 contemplates nodes 12 using any suitable techniques foraggregating power level variations along light paths to select betweenand/or configure for communication on a light path.

FIG. 2 is a block diagram illustrating exemplary functional componentsof node 12, which includes a pre-amplifier 30, a de-multiplexer 32, anoptical cross-connect fabric 34, a multiplexer 36 and a post-amplifier38. In addition, node 12 includes a controller 40 and a memory 42maintaining power level information that includes add data 44, throughdata 46, and drop data 48. Node 12 also includes spectrum analyzer units(SAUs) 62 and power monitors 64 for use in measuring power levelvariations along various channels and routes. In general, node 12supports power level management of optical communications using powerlevel information stored in add data 44, through data 46, and drop data48. More specifically, node 12 exchanges information with other nodes 12to permit selection, provisioning, and configuration of light pathsbased on aggregate power level variations calculated across light paths.

In the embodiment illustrated, node 12 provides a number of inputs andoutputs. These include an input fiber 50 and an output fiber 52 thatcouple node 12 to other nodes 12 within network 14. Node 12 alsoincludes drop fiber 54 and add fiber 56 that couple to othercommunications equipment, such as devices 16. In addition, node 12includes a control line 60 for exchanging management messages with othercommunications equipment, such as other nodes 12 and devices 16.However, while control line 60 is illustrated as a distinct input/outputline, management communications may take place between node 12 and otherequipment through any appropriate inputs and outputs, such as an opticalsupervisory channel (OSC). Moreover, while input fiber 50 and outputfiber 52 are described as coupling to other nodes 12 and drop fiber 54and add fiber 56 are described as coupling to other communicationsequipment, system 10 contemplates node 12 coupling various opticalinputs and outputs to any other appropriate optical communicationsequipment. For example, add fiber 56 may receive input generated andcommunicated along output fiber 52 of another node 12.

Pre-amplifier 30, de-multiplexer 32, optical cross-connect fabric 34,multiplexer 36, and post-amplifier 38 represent traditional componentsfor supporting optical communications. Using input fiber 50, node 12receives optical signals communicated on any number of differentwavelengths. Each of these received signals may be passed through node12 and retransmitted on output fiber 52 or “dropped” and transmitted ondrop fiber 54. Node 12 may also receive one or more optical signals atvarious wavelengths using add fiber 56. Node 12 may introduce thesesignals into the traffic of network 14 by transmitting the signals onoutput fiber 52.

In the embodiment illustrated, the table within memory 42 that maintainsadd data 44, through data 46, and drop data 48 is expanded. Thisdemonstrates a potential technique for maintaining power levelvariations for adding, dropping, and passing through optical signals ata number of different wavelengths. Add data 44 maintains power levelvariations for optical signals received on add fiber 56 and transmittedon output fiber 52. For each wavelength, this power level variationbetween signals received on add fiber 56 and signals transmitted onoutput fiber 52 represents the add power level variation. According toparticular embodiments, add power level variation is defined as thepower variation from the output of a transmitter coupled to add fiber 56to the input of post-amplifier 38. The add power level variation may bemeasured for each of the wavelengths serviced by node 12. Thus, forexample, if node 12 provides N wavelengths for the transmission ofsignals, node 12 may measure N add power level variations. Node 12maintains values for each of these power level variations within adddata 44.

To measure add power level variations, node 12 may communicate withneighboring communications equipment, such as other nodes 12 and/ordevices 16. For example, node 12 may link to the output of device 16using add fiber 56. Using an OSC, node 12 may exchange information withdevice 16 to determine the power level variation that occurs across addfiber 56. Node 12 sums this value with variations due to internaloperations to determine an add power level variation. Thus, the addpower level variation will reflect power level variation from the outputof device 16 to the input of post-amplifier 38. To populate the tablewith add data 44, node 12 cycles through each channel, measuring the addpower level variation and recording this value within add data 44.However, node 12 may determine each value at any appropriate time ortimes.

Similar to measurements for add power level variations, through powerlevel variations and drop power level variations may be measured forother paths through node 12. Through data 46 reflects the measured powerlevel variations at the various wavelengths serviced by node 12 betweensignals received on input fiber 50 and transmitted on output fiber 52.Likewise, drop data 48 maintains measured power level variations at eachwavelength serviced by node 12 between signals received on input fiber50 and transmitted on drop fiber 54. According to particularembodiments, through power level variation is defined as power variationmeasured along a particular channel between an output coupled to inputfiber 50 and the input of post-amplifier 38. Similarly, drop power levelvariation is defined as the power level variation on a particularchannel between the output of pre-amplifier 30 and the input of areceiver coupled to drop line 54.

To measure through and drop power level variations, node 12 usestechniques similar to those described above with respect to measurementsof add power level variations. For example, using communications withneighboring network equipment, node 12 can develop the entries in thetable that reflect add, drop, and through power level variations foreach wavelength serviced by node 12. Therefore, add data 44, throughdata 46 and drop data 48 maintain power level variations for thedifferent pathways for optical signals passing through node 12.

However, while specific definitions for add, through, and drop powerlevel variations are described above, system 10 contemplates using anyappropriate definitions for add, through, and drop power levelvariations based upon appropriately designated beginning and end points,so long as those definitions permit the aggregation of power levelvariations along light paths. Moreover, system 10 contemplates node 12determining and/or updating power level information at any appropriatetimes using any suitable techniques. According to particularembodiments, node 12 uses spectrum analyzer units 62 and power monitors64 to periodically, sporadically, and/or continuously monitor powerlevel variations for adding, dropping, and passing through opticalsignals.

Controller 40 represents any suitable processor, controller, and/orsuitable logic device for communicating power level information withother nodes 12 to enable power level management using aggregate powerlevel variations along light paths. In the embodiment illustrated,controller 40 links to other communications equipment using control line60. Through control line 60, controller 40 may exchange managementmessages, such as MPLS messages, with other communications equipment,such as other nodes 12. For example, through control line 60, controller40 can exchange various messages with other nodes 12 to support thecalculation of aggregate power level variations along light paths.However, as previously discussed, nodes 12 may use any suitable links toexchange management messages. For example, nodes 12 may use in-bandsignaling along communication channels, an optical supervisory channel(OSC), or any other appropriate link to exchange management messages.

In operation node 12 may function simultaneously as an add node, throughnode and/or drop node for one or more light paths. As an add node, node12 may initiate path setup messages and use responses to select lightpaths and configure for operation. As a through node, node 12 respondsto various messages, sharing through data 46 to aid in establishment oflight paths. As a drop node, node 12 responds to path setup messages bysharing drop data 48 in responses. Moreover, as a drop node, node 12 mayalso monitor active light paths and manage protection and/or restorationin the event of failures. Thus, power level information stored in Memory42 represents an important functional aspect of node 12, whetheroperating as an add node, through node, and/or drop node.

While the embodiments illustrated and the preceding description focus ona particular embodiment of node 12 that includes specific elements,system 10 contemplates node 12 having any suitable combination andarrangement of elements for sharing power variation information toenable power level management of light paths using aggregate power levelvariations. Thus, the modules and functionalities described may becombined, separated, or otherwise distributed among any suitablefunctional components, and some or all of the functionalities of node 12may be performed by logic encoded in media, such as software and/orprogrammed logic devices.

FIG. 3 is a diagram illustrating exemplary values for power levelvariations along two potential light paths from a first node 12 (node L)to a second node 12 (node M). Along each light path, exemplary valuesare given for add, through, and drop power level variations at eachappropriate step. In addition, values for variations across connectingfiber segments are also provided (transmission power level variations).Thus, in this example, add, drop, and through values represent internalvalues that may be supplemented by the values for transmission powerlevel variations. In the embodiment illustrated, light path 1 and lightpath 2 represent two potential light paths between node L and node M.Each of these light paths pass through a number of intermediate nodes12, including node N, which is common to both light paths. At node N,light path 1 is routed through an add fiber, while light path 2 isrouted through node N, thus, the values provided for power levelvariations along each light path reflect these routes.

To determine the aggregate power level variations for each light path,nodes 12 may use techniques such as those discussed above. For example,node L may communicate a path setup message along each of light path 1and light path 2, with each message accumulating values for power levelvariations as it propagates along a light path. Thus, the aggregatepower level variation for each light path will reflect add, through,drop, and transmission power level variations for appropriate nodes 12and traversed fibers.

Using replies reporting these aggregate power level variations, node Lmay select and configure to provide suitable signals for reception bynode M. For example, given the values provided in this illustration andassuming an algorithm that selects the smallest power level variation,node L will select light path 1. However, as previously discussed,system 10 contemplates nodes 12 using any suitable techniques fordetermining aggregate power level values and selecting between potentiallight paths based upon these values. Moreover, the example illustratedand accompanying description are provided only to clarify the operationof a particular embodiment.

FIG. 4 is a flowchart illustrating a method for node 12 to determine anduse aggregate power level variations for potential light paths to aremote node 12. Node 12 receives a request to establish an optical pathto a remote drop node 12 at step 100. Node 12 then, at steps 102 to 112,identifies potential light paths and initiates the determination ofaggregate power level variations on these light paths. Node 12determines an available light path to the drop node at step 102 andreserves the resource to the next node 12 for the light path at step104. For example, node A may identify an available light path to node Bthat passes through node C and reserve the channel on the fiber segmentfrom node A to node C. By reserving the resource, node A ensures thatthe potential channel will remain available until a decision is madewhether or not to use the associated light path.

Node 12 determines the add power level variation for the light path atstep 106. For example, node 12 may access add data 44 stored withinmemory 42 to determine the add power level variation for the channelassociated with the light path. Node 12 then generates a path setupmessage indicating the determined add power level variation at step 108and communicates the message to the next node 12 for the light path atstep 110. For example, as previously discussed, node A may generate anMPLS message incorporating the add power level variation and communicatethe message to node C.

Node 12 determines whether all available light paths to the drop node 12have been identified at step 112. If not, node 12 continues to identifyavailable light paths and generate path setup messages for these lightpaths. Thus, in the embodiment illustrated in this flowchart, node 12can potentially identify all light paths available for establishing anoptical communication link with drop node 12. However, system 10contemplates node 12 using any suitable algorithms for limiting thelight paths selected for consideration. For example, according toparticular embodiments, nodes 12 each maintain information detailingtopography of some or all of network 14 and use this information toidentify potential routes between nodes 12.

At steps 114 to 128, node 12 receives and processes replies to pathsetup messages. Thus, node 12 determines whether a reply to a setupmessage has been received at step 114. If so, node 12 determines whetherthe reply indicates unavailability of the light path indicated in thepath setup message. For example, while a particular channel may beavailable between node A and node C for a light path, node C maydetermine that a corresponding channel between node C and node F isunavailable. In response, node C may inform node A of the unavailabilityof the light path. In response to a reply indicating light pathunavailability, node 12 releases the reserved resource at step 118.Thus, since the resource to the next node 12 will not be used for thiscommunications link, node 12 can release the reservation so that theresource may be used for other links.

If the reply does not indicate unavailability of the light path, thenthe reply indicates an aggregate power level variation for the lightpath. Using the aggregate power level variation in the reply, node 12determines an appropriate configuration. For example, node 12 maydetermine the power level and/or variable attenuation settings thataccommodate for the indicated aggregate power level variation to providesuitable signals for reception by drop node 12. If the determinedsettings are not within the range of node 12, then node 12 will not usethis light path. Thus, if the settings are out of range, node 12 willrelease the resource reserved for this light path at step 118. Inaddition, node 12 may inform intermediate nodes 12 to release anyreserved resources for the light path.

However, if the settings are within range, node 12 determines whetherthe setting are the most favorable calculated at step 124. In thisprocess, node 12 attempts to identify the most favorable light pathbased upon aggregate power level variations and/or determinedconfigurations. As previously discussed, node 12 may use any suitablealgorithms, target values, and/or calculations to determine whether onelight path is more favorable than another. If the light path is not themost favorable, node 12 releases the resource at step 118 and, inaddition, may inform intermediate nodes 12 to release correspondingresources. However, if the light path is the most favorable, node 12selects the light path as the current selection at step 126. Node 12continues this process until replies to all path setup messages havebeen received (or some other suitable event, such as a time out). Thus,node 12 determines whether additional replies remain outstanding at step128 and, if so, continues monitoring for replies at step 114.

Upon receiving all appropriate replies, node 12 determines whether alight path has been selected at step 130. This determines whether one ofthe potential light paths identified was available and had an aggregatepower level variation indicating settings within the range of node 12.If not, node 12 may report an error at step 132. For example, node 12may generate an error message and communicate the message to the devicethat requested the optical communication link. However, if a light pathhas been selected, node 12 ensures that all unused resources arereleased at step 134 (including notifying intermediate nodes 12 torelease unused resources). Node 12 configures for the selected lightpath at step 136. For example, node 12 may configure components toprovide the power levels and/or variable attenuations determined for theselected light path. Node 12 then establishes communications on theselected light path at step 138.

The preceding flowchart illustrates only an exemplary method ofoperation, and system 10 contemplates nodes 12 using any suitabletechniques and elements for identifying potential light paths and usingpower level variation information received from other nodes 12 to selecta light path for communication. Thus, many of the steps in thisflowchart may take place simultaneously and/or in different orders thanas shown. In addition, node 12 may use methods with additional steps,fewer steps, and/or different steps, so long as the methods remainappropriate.

FIG. 5 is a flowchart illustrating a method for node 12 to share powerlevel information with other nodes 12. Thus, this flowchart details theoperation of node 12 as a potential intermediate node of a light path.Node 12 monitors received management messages at step 150. For example,node 12 may monitor MPLS messages received from other nodes 12 usingcontrol line 60. In this flowchart, the method provides processing forpath setup messages and replies indicating failure to establish a lightpath. Node 12 determines whether a setup failure reply has been receivedat step 152. Node 12 may receive this reply in a variety of scenarios.For example, node C may, after receiving a path setup message from nodeA, communicate a similar path setup message to node F. If node Fdetermines that no corresponding channel is available between node F andnode I, node F may communicate a setup failure message to node C. Node Cmay also receive setup failure messages from node A. For example, upondetermining not to use a particular light path through node C, node Amay inform node C of the failure.

In response to receiving a setup failure reply, node 12 releases anyreserved resources at step 154. In addition, node 12 communicates thesetup failure message to the previous node 12 in the light path at step156. (Or communicates the setup failure message to the next node 12 inthe light path as appropriate.) This permits all nodes 12 to releasereserved resources when appropriate.

In response to detecting a path setup message at step 158, node 12determines whether the next segment for the indicated light path isavailable at step 160. For example, upon receiving a path setup messagefrom node A indicating a particular channel, node C may determinewhether a corresponding channel is available on the fiber between node Cand node F. If node 12 determines that the next segment for theindicated light path is unavailable, node 12 communicates a setupfailure message to the previous node in the light path at step 156.However, if the segment is available, node 12 reserves the resource atstep 162.

Node 12 also determines through power level variation for the channelindicated in the path setup message at step 164. For example, node 12may access through data 46 maintained in memory 42 to determine thevalue indicated for the particular channel. Node 12 adds this value tothe power level variation indicated in the path setup message at step166. Therefore, the value indicated in the path setup message willreflect the aggregate power level variation up to and through thecurrent node 12. Node 12 communicates the path setup message to the nextnode 12 in the light path at step 168. This technique permitsdistribution of processing and data maintenance that providesscalability while retaining network level power level management.

However, as with the earlier described flowchart, the precedingflowchart illustrates only an exemplary method of operation. Thus, manyof the steps in this flowchart may take place simultaneously and/or indifferent orders than as shown. In addition, node 12 may use methodswith additional steps, fewer step, and/or different steps, so long asthe methods remain appropriate.

FIG. 6 is a flowchart illustrating a method for node 12 to determine andshare power level variations for power level management of light pathsacross network 14. This flowchart focuses in particular upon theoperation of node 12 as a drop node for a communication path. Node 12monitors received management messages at step 200 to determine whether apath setup message has been received at step 202. Upon receiving a pathsetup message indicating node 12 as a drop node, node 12 determines droppower level variation for the indicated light path at step 204. Forexample, node 12 may access drop data 48 maintained in memory 42 todetermine a value for drop power level variation on the channelidentified within the path setup message. Node 12 adds the drop powerlevel variation to the aggregate power variation value indicated in thepath setup message at step 206. Thus, at this point, node 12 hasdetermined the aggregate power level variation for the entire light pathfrom the originating add node 12 to drop node 12. Node 12 generates areply indicating this aggregate power level variation at step 208 andcommunicates the reply message to add node 12 at step 210.

However, as with the earlier described flowcharts, the precedingflowchart illustrates only an exemplary method of operation. Thus, manyof the steps in this flowchart may take place simultaneously and/or indifferent orders than as shown. In addition, node 12 may use methodswith additional steps, fewer step, and/or different steps, so long asthe methods remain appropriate.

FIG. 7 is a flowchart illustrating the operation of node 12 inmonitoring for and responding to failure of a light path. The chartfocuses in particular upon the operation of node 12 operating as a dropnode. Node 12 monitors active light paths at step 220. For example, aspreviously discussed, node 12 may monitor for the continuous receipt oflight along each light path currently in use. Upon detecting a failureof a light path at step 222, node 12 initiates messaging to reestablishthe communication link while further providing power level managementfor the backup/protection light path.

In the embodiment illustrated by this flowchart, node 12 attempts toreestablish the communication link using a dedicated protection lightpath. Node 12 determines a drop power level variation for the protectionlight path at step 224. Node 12 generates a protection path setupmessage indicating the determined drop power level variation at step 226and communicates the setup message to the previous node 12 in theprotection light path at step 228. As previously discussed, this messagethen propagates in reverse along the light path accumulating power levelvariations along the way. Thus, this message eventually provides noticeto the originating add node 12 of the failure while further providinginformation suitable for reestablishing the communication link on theprotection light path with appropriate configurations.

The preceding flowcharts and accompanying description illustrate onlyexemplary methods of operation, and system 10 contemplates nodes 12using any suitable techniques and elements for operating as add nodes,drop nodes and through nodes. Thus, many of the steps in theseflowcharts may take place simultaneously and/or in different orders thanas shown. For example, since each node 12 may simultaneously operate asan add node, drop node, and/or through node, a single node 12 maysimultaneously perform many of the techniques illustrated by theseflowcharts. In addition, nodes 12 may use methods with additional steps,fewer steps, and/or different steps, so long as the methods remainappropriate.

Although the present invention has been described in severalembodiments, a myriad of changes and modifications may be suggested toone skilled in the art, and it is intended that the present inventionencompass such changes and modifications as fall within the scope of thepresent appended claims.

1. A method for power level management of optical communications, themethod comprising: receiving a plurality of path setup messagescorresponding to a plurality of light paths from a remote optical node,each of the path setup messages identifying one of the light paths andindicating a power level variation value for the identified light path;and for each of the path setup messages: determining drop power levelvariation for the light path identified in the path setup message;adding the drop power level variation to the power level variation valuein the path setup message to obtain an aggregate power level variationfor the identified light path; generating a setup reply messageindicating the identified light path and the aggregate power levelvariation for the light path; and communicating the setup reply messageto the remote optical node.
 2. The method of claim 1, further comprisingmaintaining drop data indicating a drop power level variation for eachof a plurality of channels.
 3. The method of claim 2, whereindetermining drop power level variation for a light path comprisesidentifying the drop power level variation corresponding to the channelfor the light path.
 4. An optical communication node comprising: across-connect fabric operable to receive optical communications from aninput fiber and an add fiber and to switch received opticalcommunications for transmission on a selected one of an output fiber anda drop fiber; and a controller operable to receive a plurality of pathsetup messages corresponding to a plurality of light paths from a remoteoptical node, each of the path setup messages identifying one of thelight paths and indicating a power level variation value for theidentified light path, the controller further operable, for each of thepath setup messages, to determine drop power level variation for thelight path identified in the path setup message, to add the drop powerlevel variation to the power level variation value in the path setupmessage to obtain an aggregate power level variation for the identifiedlight path, to generate a setup reply message indicating the identifiedlight path and the aggregate power level variation for the light path,and to communicate the setup reply message to the remote optical node.5. The node of claim 4, further comprising: a first optical amplifiercoupled to the cross-connect fabric and operable to receive opticalcommunications from the input fiber; and a second optical amplifiercoupled to the cross-connect fabric and operable to transmit opticalcommunications on the output fiber.
 6. The node of claim 5, furthercomprising a memory maintaining drop data indicating a drop power levelvariation for each of a plurality of channels.
 7. The node of claim 6,wherein the drop power level variation for a channel indicates variationin power for the channel between an output of a device coupled to theinput fiber and an input of a device coupled to the drop fiber.
 8. Thenode of claim 6, wherein the controller determines drop power levelvariation for a light path by accessing the memory to identify the droppower level variation corresponding to the channel for the light path.9. Computer logic for power level management of optical communications,the computer logic encoded in computer readable media and operable whenexecuted to: receive a plurality of path setup messages corresponding toa plurality of light paths from a remote optical node, each of the pathsetup messages identifying one of the light paths and indicating a powerlevel variation value for the identified light path; and for each of thepath setup messages: determine drop power level variation for the lightpath identified in the path setup message; add the drop power levelvariation to the power level variation value in the path setup messageto obtain an aggregate power level variation for the identified lightpath; generate a setup reply message indicating the identified lightpath and the aggregate power level variation for the light path; andcommunicate the setup reply message to the remote optical node.
 10. Thecomputer logic of claim 9, further operable to maintain drop dataindicating a drop power level variation for each of a plurality ofchannels.
 11. The computer logic of claim 10, further operable todetermine drop power level variation for a light path by identifying thedrop power level variation corresponding to the channel for the lightpath.
 12. An optical communication node comprising: means for receivinga plurality of path setup messages corresponding to a plurality of lightpaths from a remote optical node, each of the path setup messagesidentifying one of the light paths and indicating a power levelvariation value for the identified light path; and means for, for eachof the path setup messages: determining drop power level variation forthe light path identified in the path setup message; adding the droppower level variation to the power level variation value in the pathsetup message to obtain an aggregate power level variation for theidentified light path; generating a setup reply message indicating theidentified light path and the aggregate power level variation for thelight path; and communicating the setup reply message to the remoteoptical node.
 13. A method for protection switching in an opticalnetwork, the method comprising: detecting failure of a light path;determining a protection light path; determining drop power levelvariation for the protection light path; generating a protection switchmessage identifying the protection light path and the drop power levelvariation; and communicating the protection switch message to a previousnode on the protection light path.
 14. The method of claim 13, whereinthe protection switch message propagates in reverse along the protectionlight path to aggregate power level variations for the protection lightpath.
 15. The method of claim 13, wherein the protection light path ispreassigned to the light path.
 16. The method of claim 13, furthercomprising maintaining drop data indicating a drop power level variationfor each of a plurality of channels.
 17. The method of claim 16, whereindetermining drop power level variation for the protection light pathcomprises identifying the drop power level variation corresponding tothe channel for the protection light path.
 18. An optical communicationnode comprising: a cross-connect fabric operable to receive opticalcommunications from an input fiber and an add fiber and to switchreceived optical communications for transmission on a selected one of anoutput fiber and a drop fiber; and a controller operable to detectfailure of a light path passing from the input fiber to the drop fiber,to determine a protection light path, to determine drop power levelvariation for the protection light path, to generate a protection switchmessage identifying the protection light path and the drop power levelvariation, and to communicate the protection switch message to aprevious node on the protection light path.
 19. The node of claim 18,further comprising: a first optical amplifier coupled to thecross-connect fabric and operable to receive optical communications fromthe input fiber; and a second optical amplifier coupled to thecross-connect fabric and operable to transmit optical communications onthe output fiber.
 20. The node of claim 19, further comprising a memorymaintaining drop data indicating a drop power level variation for eachof a plurality of channels.
 21. The node of claim 20, wherein the droppower level variation for a channel indicates variation in power for thechannel between an output of a device coupled to the input fiber and aninput of a device coupled to the drop fiber.
 22. The node of claim 18,wherein the protection switch message propagates in reverse along theprotection light path to aggregate power level variations for theprotection light path.
 23. The node of claim 18, wherein the protectionlight path is preassigned to the light path.
 24. Computer logic forprotection switching in an optical network, the computer logic encodedin computer readable medium and operable when executed to: detectfailure of a light path; determine a protection light path; determinedrop power level variation for the protection light path; generate aprotection switch message identifying the protection light path and thedrop power level variation; and communicate the protection switchmessage to a previous node on the protection light path.
 25. Thecomputer logic of claim 24, further operable to maintain drop dataindicating a drop power level variation for each of a plurality ofchannels.
 26. The computer logic of claim 25, further operable todetermine drop power level variation for the protection light path byidentifying the drop power level variation corresponding to the channelfor the protection light path.
 27. An optical communication nodecomprising: means for detecting failure of a light path; means fordetermining a protection light path; means for determining drop powerlevel variation for the protection light path; means for generating aprotection switch message identifying the protection light path and thedrop power level variation; and means for communicating the protectionswitch message to a previous node on the protection light path.
 28. Amethod for power level management of optical communications, the methodcomprising: in a first mode of operation: receiving a request toestablish a communication channel with a remote optical node;determining a next node for a light path to the remote optical node;determining add power level variation for the light path; generating apath setup message identifying the light path and the add powervariation; and communicating the path setup message to the next node; ina second mode of operation: receiving a second path setup message thatidentifies a second light path between an add node and a drop node, thesecond path setup message comprising a power level variation value;determining through power level variation for the second light path;adding the through power level variation to the power level variationvalue in the second path setup message; and communicating the secondpath setup message to a next node in the second light path; and in athird mode of operation: receiving a third path setup message, the thirdpath setup message identifying a third light path and indicating a powerlevel variation value for the third light path; determining drop powerlevel variation for the third light path; adding the drop power levelvariation to the power level variation value in the third path setupmessage to obtain an aggregate power level variation for the third lightpath; generating a setup reply message indicating the third light pathand the aggregate power level variation; and communicating the setupreply message to a remote add node for the third light path.